Method of blowing reducing gas into a blast furnace

ABSTRACT

METHOD FOR BLOWING A REDUCING GAS INTO A BLAST FURNACE IN WHICH THE REDUCING GAS IS PRODUCED IN A REDUCING GAS GENERATOR, SUPPLYING GASEOUS MATERIALS INTO THE REDUCING GAS GENERATOR UNDER SPECIFIC CONDITIONS WITH THE TEMPERATURE OF THE PRODUCED GAS CONTROLLED AND THE TEMPERATURECONTROLLED GAS BEING BLOWN IN THE BLAST FURNACE.

Sept. 18, 1973 KAZUO QMQR] EI'AL 3,759,698

METHOD OF BLOWING REDUCING GAS INTO A BLAST FURNACE;

Filed Nov. 13, 1969 '7 Sheets-Sheet 1 when the blast furnace has atendenc of Banging (a) (A) (Q) (A) I I I Z0 Blast furnace Pressure atblow-in opening level V g/cm G) m Gas pressure in JJ reducing gasgenerator s/curs) Oxygen flow rate 4120 (Nm /H) Steam flow rate da (Nm7H) v produced ('0 4 R-value of gas /9 produced 7 a INVENTOR 0 1 ZTime(min) Yfl fl fim nan BY Hnsnnm lGlUH J! 8 Dig ATTORNEY l 1973 KAZUOOMORI ETAL 3,759,698

METHOD 0f" BLOW'ING REDUCING GAS INTO A BLAST FURNACE Filed Nov. 15,1969 7 Sheets-Sheet 2 When blow-in opening has 0 tendency of clogging i7 Z 6 d) g /fifl Blow-in resistance 4 Pressure in gas generator 4 /cm G)Oxygen flow fflpfi 5 (Nm m) 40W Jana Steam flow /m aw Temperature ofZ000 gas produced flu!) /Zaa R-value of gas /fl produced increase ofincrease of (f unbumt constituents unburnt constituents mcrese ofunburnt fl constituentsand danger of explosion overheatmg I l l I 4 ZTime INVENTOR Knzuo 0mm YOSIHRtKI HHRR BY Mnsnnm IGUCIH d4 7 5m ATTORNEYSept. 18, 1973 KAZUO QMOR] ETAL 3,759,698

METHOD OF BLOWING REDUCING GAS INTO A BLAST FURNACE Filed Nov. 13, 1969'T Sheets-Sheet 5 19 km) (A) Blast furnace Z9 Pressure ot blow-inopeninglevel Gus pressure in reducing gas generator /cm G) (Nm /H) Steamflow rate 0V0 Nm H W K 7 I I Temperature ofgos /7fl/7 produced ("0,Zflfl R-volue of 905 g produced a: W

ATTORNEY Sept. 13, 1973 KAZUO OMORI ETAL 3,759,698

METHOD OF BLOWING REDUCING GAS INTO A BLAST FURNACE Filed Nov. 13, 1969'7 Sheets-Sheet 4.

Blow-in resistance J'fl Pressure in gas enerator 4 Q/cm G) Oxygenflow/flflp /H) Steam flow 700 (N /H) 5 1 Temperaiure of [My gas produced('6) M00 R-va1ueof gas m MWMWM produced 0 I I I l T INVENTOR lrne KHZU 0onom yasnmm IIRRH BY hnsnnm legal ATTORNEY p 1973 v KAZUO OMORl E L3,759,698

METHOD OF BLOWlNG REDUCING GAS lNTO A BLAST FURNACE Filed Nov. 13, 196i)'7 Sheets-Sheet l,

Utility efficiency 0.6 e

of hydrogen Reducing gas Temp Z (natural gas) Flow rate Q/Cm H)Down-stream Pressure/ UP Stream P ressure Critical Pressure flia natural5 who my 9 ajdfl R/ 004 steam ygen JJZfl Specific heal ratio INVENTORknzuo 0mm yosmnm umzn nnsanm leucm BY life 1L ATTORNEY Sept. 18, 1973 VKAZUO OMQRI ETAL 3,759,698

METHOD OF BLOWING REDUCING GAS INTO A BLAST FURNACE Filed Nov. 13, 19697 Sheets-Sheet 6 INVENTOR KHZUO OMDRI yosumm HnRn BY flnsnnm IGUCHI I 9%3 21! ATTORNEY Sept. 18, 1973 A KAZUO OMOR] ETAL 3,759,698

METHOD OF BLOWING REDUCING GAS INTO A BLAST FURNACE Filed Nov. 15, 1969'7 Sheets-Sheet 7 ,L/ INVENTOR A kHZuo 0mm a OSHIBKI "HRH HSHPKI IGUCHIATTORNEY United States Patent 3,759,698 METHOD OF BLOWING REDUCING GASINTO A BLAST FURNACE Kazuo Omori, Yoshiaki Hara, and Masaaki Iguchi,Himeji-shi, Japan, assignors to Fuji Iron & Steel Co., Ltd., Tokyo,Japan Filed Nov. 13, 1969, Ser. No. 876,535 Claims priority, applicationJapan, Nov. 20, 1968, 43/85,013, 43/ 85,014; Feb. 20, 1969, 44/ 12,867,44/ 12,868, 44/8,845

Int. Cl. C22b /00 US. CI. 75-42 6 Claims ABSTRACT OF THE DISCLOSUREMethod for blowing a reducing gas into a blast furnace in which thereducing gas is produced in a reducing gas generator, supplying gaseousmaterials into the reducing gas generator under specific conditions withthe temperature of the produced gas controlled and thetemperaturecontrolled gas being blown in the blast furnace.

This invention relates to a method of blowing a reducing gas, producedoutside of a blast furnace, into the blast furnace in order to reducethe consumption of coke in the blast furnace and to increase itsproductivity.

The method of producing reducing gas outside of a blast furnace andblowing the gas into the blast furnace has already been proposed.However, there are many prob lems to be solved in such a method, andaccordingly, the method has not yet been commercially worked.

The first problem lies in the fluctuation of the composition andtemperature of the gas produced owing to the variation of the furnacepressure of the blast furnace.

Even when the furnace pressure of the blast furnace is constant, theblow-in resistance (the resistance against the blowing of reducing gasinto the blast furnace) fluctuates owing to the changes in the particlesize and softening condition of the burden near the blow-in opening ofthe furnace, and also to the stick-to and strip-off of the burden aroundthe blow-in opening. The fluctuation of the blow-in pressure spreadsthrough the reducing gas pipe lines connecting the blow-in opening andthe reducing gas generator; and finally, the fluctuation of the pressureof the reducing gas generator takes place. As a result, among the rawmaterials supplied to the reducing gas generator, i.e., the fuel (solid,liquid, gas), the oxidant (air, oxygen) and steam, the supply of thecompressible gaseous raw materials (gaseous fuel, oxidant and steam)fluctuates remarkably, which causes the fluctuation of the compositionand temperature of the reducing gas produced.

For instance, when the blow-in resistance to the reducing gas of theblast furnace increases suddenly, while the solid or liquid fuel issupplied constantly through the pump, the supply of the oxidant andsteam diminishes; and consequently the unburnt constituents (soot,methane, etc.) increases, and the temperature of the reducing gasgenerator decreases suddenly.

When the blow-in resistance decreases suddenly, a large quantity of theoxidant and steam is supplied instantaneously, and the fuel burnsexplosively, which leads sometimes to an explosion. When thecharacteristics of the flow controlling apparatuses for the rawmaterials do not coincide with each other, a similar phenomenon mayoccur with the use of gaseous fuel. Even if the explosion does notoccur, since much heat is produced by the excess combustion mentionedabove, the temperature of the re ducing gas generator increases; and notonly the generator lining but also the burner of the generator aredamaged by melting, and consequently the operation of the reducing gasgenerator becomes difiicult, and it is impossible to blow the reducinggas into a blast furnace.

Owing to the change of the quantity and proportions of the raw materialssupplied, the fluctuation of R-value which expresses the reducing powerof the gas) and temperature of the reducing gas produced takes place.When such a fluctuating gas is blown into the blast furnace, thereducing condition of the blast furnace, particularly the utilizationefiiciency of hydrogen is changed, and the gaspermeability of thefurnace is also altered. Due to the change in reducing condition, thebehavior of silicon in the pig iron becomes unstable, the descendingcondition of the burden is disturbed, and the smooth operation of theblast furnace becomes impossible.

The present invention shall be described in detail referring to theattached drawings in which:

FIGS. 1-4 are explanatory drawings showing the relation between thepressure variation in a reducing gas generator and the temperature andR-value of the reducing gas produced. The method of supplying rawmaterials to the reducing gas generator is referred to by (a) and thefurnace condition of the blast furnace is referred to by (b) in FIGS. 1to 4 as follows:

FIG. 1 (a): controlled by a conventional method, (b): the blast furnacehas a tendency of hanging and slipping;

FIG. 2. (a): as in FIG. 1, (b): the blow-in opening of the reducing gashas a tendency of clogging;

FIG. 3 (a): according to the method of this invention, ([1): as inFIG.1;

FIG. 4 (a): as in FIG. 3; (b): as in FIG. 2;

FIG. 5 is an explanatory drawing showing the relation between thetemperature of reducing gas blown-in and the utility efliciency ofhydrogen;

FIG. 6 is an explanatory drawing showing the critical pressure ratio inthe case of, for example, natural gas used as a gaseous raw material;

FIG. 7 is an explanatory drawing showing the relation between thespecific heat ratio and the critical pressure ratio of gaseous rawmaterials;

FIG. 8 is a flow-sheet of an apparatus used in working the presentinvention;

FIG. 9 is an explanatory drawing of an example of the apparatus forsupplying raw materials, attached to the reducing gas generator of thisinvention;

FIGS. 10-14 are flow-sheets of examples of a reducing gas blow-intemperature controlling apparatus used in this invention, in which thegas is cooled by mixing with a low temperature reducing gas, where;

FIG. 10 is a flow-sheet using a partial flow of the high temperaturereducing gas produced.

FIG. 11 is a flow-sheet using a low temperature reducing gas obtainedfrom a separate source;

FIG. 12 is a flow-sheet using the apparatus in FIG. 10 together with awaste heat boiler;

FIG. 13 is a flow-sheet using the apparatus in FIG. 12 together with awaste heat boiler; and

FIG. 14 is an explanatory drawing showing the crosssection of an exampleof a rapid cooler used in this invention.

As for the first problem mentioned above, the actual problem in the caseof supplying the gaseous raw materials by the usual flow controllingsystem and supplying heavy oil as the fuel by a constant-volume pumpwill be described referring to FIG. 1 and FIG. 2.

FIG. 1 shows the fluctuating relationship between the furnace pressureof the blast furnace and the temperature and R-value of the gas producedin the reducing gas generator when the blast furnace has a tendency ofhanging and slipping.

As seen from the figure, when the furnace pressure of the blast furnaceincreases gradually as shown by (a) in the figure at the commencement ofhanging, the usual controlling apparatus responds sufliciently, and thesupply of gaseous raw materials can be maintained almost constant.However, when the furnace pressure decreases beyond the responsibilityof the controlling apparatus as shown by (b) at the time of theslipping, the balance of the supply of the fuel, the combustion promoterand the water vapour is destroyed instantaneously, and the fluctuationof the temperature and R-value of the gas produced takes place.Particularly, once such a sudden change of the temperature takes place,a more serious problem ocours as mentioned below.

FIG. 2 shows the fluctuating relationship between the blow-in resistanceand the temperature and R-value of the reducing gas produced at the timewhen the blow-in opening of the reducing gas has a tendency to clog.

When the temperature of the reducing gas to be blowin is higher thanthat of the softening point of the burden of the blast furnace, theburden near the blow-in opening is melted partially and becomes sticky,and as a result, it clogs the blow-in opening, and the blow-inresistance increases suddenly Then, the flow of the oxidant and steamdecreases suddenly. However, when the sticky block of molten burdenleaves from the blow-in opening, the blow-in resistance decreasessharply (d), and consequently, the flow rate of the combustion promoterand steam increases suddenly. When the change of the blow-in resistanceis rapid and remarkable, the fluctuation in the supply of gaseous rawmaterials above-mentioned continues for a while, although the deviationfrom the preset value diminishes gradually; and consequently, thetemperature and R-value of the gas produced fluctuate remarkably.

When the blow-in resistance fluctuates suddenly in this way, thegenerator operating condition becomes quite dangerous. The unburntconstituents in the gas produced, increase owing to the increase of theblow-in resistance; and, in such a situation, when the supply of theoxidant increases owing to the decrease of the blow-in resistance, alarge quantity of the unburnt constituents mentioned above burnexplosively. When such a condition is repeated, an explosion takesplace; the reducing gas generator is broken, and it may result in ahuman disaster.

As is obvious from the above explanations, unless the first problem issolved, it is impossible to blow the reducing gas into the blast furnacesteadily.

The second problem is that the temperature of the reducing gas, producedeconomically and efliciently in the reducing gas generator, is generallyhigher than the operatively acceptable upper limit for blowing thereducing gas into the blast furnace; and moreover, as the acceptableblow-in temperature of reducing gas into the blast furnace changes dueto the variety of the raw materials to be charged in the blast furnace,and due to their mixing ratio and the furnace condition, this blow-intemperature should be controlled in correspondence with the acceptabletemperature of the blast furnace, while the blow-in temperature ofreducing gas into the blast furnace cannot be controlled sufliciently bythe cooling with a conventional waste heat boiler.

As for the reducing gas useful for the blast furnace, it is necessarythat the R-value is greater than 3, or, for instance, when heavy oil isused as the fuel, the unburnt constituents should be 14% (weightpercentage to the carbon in the fuel). When such a reducing gas isproduced economically and efliciently, the temperature of the gasproduced is usually higher than 1400 C. On the other hand, as seen fromthe efliciency of the reducing gas blowin based on the utilityefiiciency of hydrogen in FIG. 5, it is sufficient if the blow-intemperature is 850 C. or above.

In FIG. 5, the vertical axis represents the utility efliciency ofhydrogen, the horizontal axis represents the reducing gas temperature,and their relation is expressed as the curve e. While the utilityefficiency of hydrogen decreases remarkably below 850 C., it is nearlyconstant above 850 C., although increasing slightly. From the standpointof the heat economy of the blast furnace, it is desirable that the gastemperature is as high as possible. However, the softening temperatureof the raw materials to be charged in the blast furnace varies in arange of about 900 C.1200 0, depending upon their types and mixingratios of burden.

Therefore, when gas with a temperature higher than the softening pointof the burden is blown in, the burden near the opening of the injectoris melted partially and becomes sticky, which prevents the gaspermeability and the normal descending action of the burden in thefurnace; and the smooth operation of the blast furnace becomesimpossible.

In a conventional waste heat boiler, as the cooling capacity isdetermined by the cooling area, even if the amount and pressure of thecooling water is controlled, the control of the cooling capacity ispractically impossible; and moreover, the cooling capacity fluctuatesowing to the deposition and strip-off of the soot in the gas on thecooling surface. Therefore, such a waste heater boiler cannot be usedfor the fine temperature control as in the present invention, in which alarge quantity of the reducing gas of a high temperature is cooled.

The third problem concerns the treatment of the gas of varyingtemperature and R-value at the startup of the reducing gas generator.

It is necessary to blow a reducing gas of nearly constant temperatureand R-value into the blast furnace when its operating condition isconstant. The fluctuation of the reducing gas disturbs the furnacecondition.

Therefore, a reducing gas of fluctuating temperature and R-value shouldbe treated safely without blowing into the blast furnace directly.

The fourth problem is the handling and treatment of the gas produced inthe reducing gas generator when the blowing of the gas into the blastfurnace is stopped for a short period.

If the production of the reducing gas in the reducing gas generator isstopped in accordance with the blowdown of the blast furnace for a shorttime in order to repair the cinder notch or the blast tuyere, variousproblems arise such as the shut-down of the reducing gas generator, thedamage of the refractory lining due to the temperature change, thetroubles in the generator operation for shut-down and start-up, thedelay of blowing the reducing gas into the blast furnace due to the timenecessary for starting operation; and consequently, the productionefficiency of the reducing gas and the blow-in efiiciency of thereducing gas into the blast furnace are lowered.

The present invention offers a method for blowing the reducing gas intothe blast furnace without the problems mentioned above.

The first object of the present invention is to provide a method ofproducing a reducing gas outside of the blast furnace and blowing thegas produced into the blast furnace, in which, the raw materialsconsisting of fuel (solid, liquid, gas), oxidant (air, oxygen) and steamare supplied into the reducing gas generator.

Among these materials the gaseous materials are passed through aflow-control apparatus and supplied to the reducing gas generatorthorough its burner. The pressure of the gaseous materials after theflow-control apparatus depends on the pressure of the reducing gasgenerator and the pressure drop in the burner, and fluctuates asmentioned before. Therefore in the present invention, the pressure ofthe gaseous materials before passing through the fiow-control apparatusis maintained constant so that the ratio of the pressure downstream ofthe flowcontrol apparatus to the pressure upstream of the flowcontrolapparatus is not more than the critcical pressure ratio used in thehydro-dynamics, and the gas produced is blown into the blast furnaceafter the gas temperature is controlled.

The second object of the present invention is to provide a method forcontrolling the blow-in temperature of reducing gas produced inattaining the first object, in which the gas is cooled by mixing with alow temperature reducing gas.

The third object of the present invention is to provide an apparatus forattaining the first object, comprising a reducing gas generator havingmeans for supplying the raw materials into the reducing gas generatorunder a constant pressure, means for controlling the reducing gasblow-in temperature, in which a high temperature reducing gas producedis adjusted to a temperature acceptable for the blast furnace condition;means for cutting otf the supply of high temperature reducing gas to theblast furnace and preventing the reverse flow of the gas from the blastfurnace; means for blowing the reducing gas into the blast furnace; pipelines connecting the above means; and branched pipe lines connected tothe above pipelines and provided with a rapid cooler and a cut oifvalve.

The fourth object of the present invention is to provide anotherapparatus for attaining the first object, comprising a temperaturecontrolling means for controlling the reducing gas blow-in temperature,in which the gas is cooled by mixing with a low-temperature reducinggas.

The following are the results of various experiments and investigationsby the present inventors to solve the four problems mentioned above.

The inventors found that, to solve the first problem, a law ofhydro-dynamics hitherto known can be applied.

It has been known that, in passing a compressible gas in a pipe linehaving a neck, when the up-stream pressure is maintained at a constantvalue, the ratio of the downstream pressure to that of the up-streambeing not more than a critical pressure ratio, the flow velocity at theneck is equal to the sonic velocity, and the flow rate can be maintainedconstant without being influenced by the fluctuation of the down-streampressure. The relation is shown in FIG. 6.

In FIG. 6, the vertical axis represents the flow rate (kg./cm. /hr.),the horizontal axis represents the ratio of the down-stream pressure tothe up-stream pressure; and by maintaining the up-stream pressureconstant, the flow rate changes with varying down-stream pressure areillustrated. It is obvious that, by increasing the up-stream pressure,the flow rate increases as shown by A, B and C. However, in every case,there are two zones; the one (D) in which the flow rate is constantwithout being influenced by the change in the down-stream pressure undera constant pressure up-stream, and the other (E) in which the flow ratechanges. The former zone lies in the range in which the ratio of thedown-stream pressure to the up-stream pressure is not more than thecritical pressure ratio (a), and the latter zone lies in the range inwhich said ratio is more than the critical pressure ratio (it).

Now through extensive experiments based on the above law for a processfor producing reducing gas constantly free from the influence of thepressure of the blast furnace, the present inventors have found that theonly commercially applicable way is to apply the above law to the supplyof gaseous materials to a reducing gas generator.

Two types of experiments were conducted by the present inventors usingthe above law.

In one type of the experiments, the ratio of the downstream pressure tothe upstream pressure is maintained in the above-mentioned D zone byproviding a neck using an orifice or a pressure controlling valve or thelike in the pipe line connecting the reducing gas generator and areducing gas blow-in opening of the blast furnace. In the other type ofexperiment, a neck using a flowcontrolling valve, an orifice or a burnernozzle or the like is provided in the pipe-line for supplying gaseousmaterials to the reducing gas generator to maintain the ratio of thedown-stream pressure to the up-stream pressure in the above-mentioned Dzone.

In the first type of experiment mentioned above, however, the presentinventors found that there are such difliculties that the damage of theneck caused by the hightemperature, and the high-velocity reducing gasflow is too small to continuously maintain the above condition, andfurther the high-pressure resistant construction of the hot gaspipe-line from the reducing gas generator up to the neck involves suchcomplexity that it prohibits a continuous supply of the reducing gasinto the blast furnace, in spite of the advantages that the temperatureand R-value of the produced gas, as Well as its volume blown into theblast furnace, can be maintained almost constant.

Whereas, in the latter type of experiment the present inventors foundthat there are no such difiiculties as met in the first type ofexperiment, and a constant production of reducing gas in combinationwith the action of a reducing gas temperature controlling apparatus asmentioned hereinafter enables a continuous blowing of the reducing gasinto the blast furnace.

One embodiment of the latter experiment in which the reducing gas isproduced by using heavy oil as fuel supplied by a constant-volume pumpshall be described referring to FIG. 3 and FIG. 4.

FIG. 3 shows, as FIG. 1, the relation between the variation in the blastfurnace pressure and the variation in the temperature and R-value of theproduced gas. When the reducing gas is produced maintaining the supplypressure of the gaseous materials such as oxygen and steam supplied intothe reducing gas generator at a constant value so that the ratio of thedown-stream pressure, to the up-stream pressure is not more than thecritical pressure ratio, even if the pressure in the balst furnace risesto such high pressure as under a furnace condition in which there is atendency of hanging and slipping. As clearly understood from thedrawing, when the pressure in the blast furnace varies considerably atthe time (a) of commence of hanging and at the time (b) of slipping,thepressure in the reducing gas generator corresponds to this and variesconsiderably.

On the other hand, the variation in the flow rate of the gaseousmaterials (oxygen and steam) supplied into the reducing gas generator isnegligible so that the variation in the temperature and R-value of theproduced gas is also negligible. This produced gas with its temperaturecon trolled was continuously blown into the blast furnace satisfactorilywithout any trouble in the production of reducing gas, in the blowing ofreducing gas into the blast furnace, as well as in the blast furnaceoperation.

FIG. 4 shows, as FIG. 2, the relation between the pressure in the blastfurnace and the temperature and R-value of the produced gas when thegaseous material is supplied and the reducing gas is produced in asimilar way as in FIG. 3 under a furnace condition in which the blow-inopening of the reducing gas has a tendency to clog.

As is clear from the drawing, when the blow-in opening is clogged with asticky block of the burden, the blow-in resistance rapidly increases andthen when the sticky block leaves the blow-in opening, the resistancerapidly decreases, and the pressure in the reducing gas generatorcorresponds to the above changes and varies considerably.

However, the variation in the filow rate of the gaseous material is verysmall so that the variation in the temperature and R-value of thereducing gas is negligible and the production of reducing gas and theblowing of reduc- I provides for the first time a novel method which canproduce reducing gas of an almost constant temperature and R-valuewithout being influenced by the variation in the pressure in the blastfurnace or by the clogging of the blow-in opening.

Critical pressure ratios of various gaseous materials are shown in FIG.7 in which the critical pressure ratios are shown along the verticalaxis and the specific heat ratios are shown along the horizontal axisand the line (f) shows the relation between the critical pressure ratiosand the specific heat ratios. As shown, natural gas has a criticalpressure ratio of about 0.55, oxygen about 0.53 and water vapour about0.54.

For controlling the thus produced high-temperature reducing gas havingconstant temperature and R-value to a temperature most acceptable for ablast furnace, a branch flow of the high-temperature reducing gasproduced in the reducing gas generator is cooled to about 40 C. by arapid cooler as shown in FIG. 14 and forced back to the high-temperaturereducing gas, or a low-temperature reducing gas separately obtained isforced into the hightemperature gas.

The present inventors found these methods for controlling thetemperature of the high-temperature reducing gas by mixing it with alow-temperature reducing gas is best for controlling quickly andprecisely a large amount of high-temperature produced reducing gas.

The temperature control of reducing gas may also be done by cooling thegas with a waste heat boiler, and further controlling the temperature ofthus cooled gas by mixing a low-temperature reducing gas asabove-mentioned corresponding to the variation in the heating capacityof the boiler and to the temperature variation required by the blastfurnace.

Next, in the present invention, in order to assure an efficient andstable production of reducing gas as well as an efiicient and stableblowing of the gas into a blast furnace, a branched pipe-line having arapid cooler is provided in the reducing gas supply pipe-line so thatthe reducing gas produced at the starting operation of the gas generatorand during the blow down of the blast furnace may be supplied or ventedto other applications.

Examples of an apparatus used in experiments and cmbodiments of thepresent invention shall be explained referring to FIG. 8-FIG. 14.

FIG. 8 shows a flow arrangement of an apparatus for working the presentinvention, in which 1 is a supplier for supplying raw materials to areducing gas generator 2. 3 is a pipe-line for supplying the reducinggas into a blast furnace. The pipeline 3 is provided with atemperaturecontrol device 4 for the reducing gas used for cooling thehigh-temperature reducing gas by mixing it with a lowtemperaturereducing gas, a cut-off valve 5 for the high temperature gas, a branchedpipeline 8 having a rapid cooler 6 and a cutoff valve 7, and anexpansion joint 9.

The supplier 1 is constructed as shown in FIG. 9 in case heavy oil, forexample, is used as fuel. 11 is a cracking furnace for heavy oil, 12 isa pipe-line for supplying oxygen, 13 is a pipe-line for supplying heavyoil and 14 is a pipe-line for supplying steam.

Both of the oxygen supply pipe-line 12 and the steam supply pipe-line 14are provided with a pressure controlling valve 15 activated by a signalfrom the pressure controller (PIC), and a flow controlling valve 16activated by a signal from the flow controller (FIC).

Oxygen and steam pass through the pipe-lines 12 and 14 respectively,while heavy oil is pumped by a constantvolume pump 17 and passes throughthe heavy oil supply pipe-line 13, and all are supplied into thecracking burner 18.

For the production of reducing gas in the heavy oil cracking furnace 11,oxygen and steam are forced into the heavy oil cracking furnace 11 whilemaintaining the supply pressure up-stream of the flow controlling valve16 or instead of the valve, an orifice (not shown) or a burner nozzle(not shown) at a constant value so that the ratio of the down-streampressure to the up-stream pressure is not more than the criticalpressure ratio (a) as defined above. In this way the temperature andR-value of the produced gas are maintained constant as shown in FIG. 3and FIG. 4 irrespective of any variation in the blast furnace pressureor the clogging of the blow-in opening.

Next, the temperature controlling apparatus 4 for the reducing gas usedfor cooling the high-temperature reducing gas by mixing it with alow-temperature reducing gas shall be described referring to FIG.10-FIG. 14.

In FIG. 10, part of the high-temperature reducing gas produced in thereducing gas generator 2 is led to a rapid cooler 21 as shown in FIG.14, in which the gas is cooled and washed by quenching it directly in acooling water (if necessary a spray cooler 22 may be used forspray-cooling and washing), then lead to a compressor 23 where the gaspressure -is increased, through a flow controlling valve 24 activated bythe signal from the temperature controller (TIC), and supplied to thepipe-line 3 to control the temperature of the high-temperature reducinggas.

Thus, it is possible to control the temperature of reducing gas to apre-set temperature without any trouble such as the variation in coolingcapacity, poor controllability of cooling temperature etc. which areoften met in using a waste heat boiler.

FIG. 11 shows a modification in which instead of cooling the branch fiowof the high-temperature reducing gas, a low-temperature reducing gas,such as a L.D. convertor gas, raw gas for ammonia-production, a blastfurnace gas, a coke oven gas, a petroleum waste gas etc. which areavailable at room temperature, is used. The above lowtemperaturereducing gas supplied separately is stored in a tank 31, and thepressure of the gas is increased by a compressor 23 and then the gas issupplied to the pipeline 3 through a flow controlling valve 24 activatedby the signal from the temperature controller (TIC). In this way, sameresults as in FIG. 10 are obtained.

FIG. 12 and FIG. 13 show respectively another modification of thetemperature controlling apparatus for the reducing gas used for coolingthe high-temperature reducing gas by mixing it with a low-temperaturereducing gas and using a waste-heat boiler 41.

In FIG. 12 a high-temperature gas from the pipe-line on the outlet sideof Waste heat boiler 41 passes through a branch pipe-line 42 to aspray-washing cooler 43 Where the gas is cooled, through the compressor23 and a flow controlling valve 24 activated by the signal from thetemperature controller (TIC) and is blown into the pipe-line 3 on theinlet side of the waste-heat boiler to control the temperature of thehigh-temperature reducing gas.

In FIG. 13, the low-temperature reducing gas supplied separately at roomtemperatures is stored in the tank 31, passes through the compressor 23and a flow controlling valve 24 activated by the signal from thetemperature controller (TIC) and is blown into the pipe-line 3 on theinlet side of the waste-heat boiler 41 to control the temperature of thehigh-temperature reducing gas.

The apparatus described referring to FIG. 12 and FIG. 13 produce similarresults as the apparatus of FIG. 10 and FIG. 11 overcoming thedeficiencies of a waste-heat boiler by controlling the temperature ofthe reducing gas with a low-temperature reducing gas.

The branch pipe-line 8 provided with the rapid cooler 6 and the cut-offvalve 7 shall be described referring to FIG. 8 and FIG. 14. Thehigh-temperature cut-ofif valve 5 is closed and the cut-off 7 is openedat the time of starting operation of the reducing gas generator 2,during the period when the temperature the R-value and the unburntconstituents of the produced reducing gas are not constant or during theperiod when the produced reducing gas cannot be blown into the blastfurnace due to a shorttime blow-down. In this way the produced gas ispassed through the rapid cooler 6 where it is cooled and vented to theatmosphere through the vent stack 67 or used as a fuel gas, or recoveredand used as a low-temperature gas for controlling the temperature of thehigh-temperature reducing gas.

The construction of the rapid cooler 6 illustrated in FIG. 8, is shownin FIG. 14 and is similar to that of the cooler 21 shown in FIG. 10.

The coolers 6 in FIG. 8 and 21 in FIG. 10 have a diiferent coolingcapacity: the former cools the gas to about 100 C., the latter cools thegas to about 40 C.

The cooler 6 shall be described referring to FIG. 14. The cooler 6comprises a cooling chamber 61 into which the end 62 of the pipe-line 8projects, a cylinder 63 is positioned about the end 62 between the endand the chamber 61 and a water-vapour separating plate 68 is providedabout the pipe-line 8 above the cylinder 63.

At the lower end of the cooling chamber 61 there is provided a waterexhaust pipe 64 having an exhaust flow controlling valve 65 activated bya signal from the liquid level controller (LIC) to control the amount ofcooling water poured from the cooling water supply pipe 66 and remainingin the cooling chamber 61.

Examples of the present invention shall be described below.

A low-temperature reducing gas cooled to 40 C. was forced into ahigh-temperature reducing gas at a flow rate of 14,000 Nmfi/hr. (Nm.means gas volume in the normal state at (3., 1 atm.) using the apparatusof FIG. to control the temperature of the high-temperature gas to 1100"C. On the other hand, a hydrogen-rich raw gas at 30 C. for ammoniaproduction of 30 C. from a separate soruce was forced into a pipe-lineon the inlet side of a waste-heat boiler at an average flow rate ofabout 6000 Nmfi/hr. and cooled in the boiler to a controlled temperatureof 1100 C. The gaseous materials of the former method (G) and the latermethod (F) were blown into a blast furnace of 1600 m Conditions forproducing reducing gas:

Blowing conditions:

Blowing position (percent) 20 35 Blowing temperature C 0.).... 1,1001,100 Blowing rate 36, 000 30,000

Blowing position (percent) means the percentage of the distance betweenthe blast tuyere and the blowing position to the distance between thetuyere and the stockllne.

As a comparative example, a reducing gas produced under the sameconditions using a conventional material supplying apparatus was cooledby a waste-heat boiler and blown into a blast furnace of 1600 m. at ablowing position of 20%, a blowing temperature of 1100 and a blowingrate of 15,000 Nm. /hr.

The following table shows results of blast furnace operations using themethod (H) of the above comparative example, the inventive methods (F)and (G) and the conventional method (K) in which a reducing gas is notblown into the blast furnace.

F G H K Reducing gas blowing availability (percent) 97. 5 97. 9 23. 8Reducing gas blowing rate (Nm lt-pig)- 195 196 28 Pig production(t./day) 3,705 3,669 3, 207 3, 218 Coke rate 418 424 485 483 Si contentin pig (percent):

X. 0. 674 0. 669 0. 733 0. 661 6 ii). 118 0. 113 0. 163 0. 105

Total time of blowing 1 Reducing gas blowing availability=-X Annual timeAs understood from the above table, in both of the inventive methods (F)and (G), the reducing gas can be blown continuously during the operationof a blast furnace, and show a remarkable eflfect in increasing the pigproduction, and reducing the coke rate. While in the comparative method(H), the temperature of the reducing gas is influenced by the pressurein the blast furnace into which the gas is blown, and this variation intemperature cannot be adjusted so that a sticky block of the burden isformed at the blow-in opening, and every time this block sticks to orleaves the openingthe explosive burning as mentioned before takes placerepeatedly in the reducing gas generator, thus increasing the danger ofexplosion. Further, the variation in the temperature of the furnaceburden and the variation in the reducing condition are large so that thebehavior of the silicon content in the pig varies largely, which causesirregular descending of the furnace burden and frequent hangings andslippings, which in turn causes sudden changes of the pressure in thereducing gas generator, and thus frequent interruption of the blowing ofthe reducing gas is unavoidable. Thus no improvement in a blast furnaceoperation can be obtained; no better than the conventional method (K),even worse than it as shown in the above example; particularly thevariation in the silicon content of the pig is sharply increased and theblast furnace operation becomes exceedingly unstable.

According to the present invention, a reducing gas having a stabletemperature and composition can be produced efliciently and economicallyin a reducing gas generator connected to a blast furnace, and thisproduced gas can be blown into the blast furnace at a controlledtemperature, thus increasing pig production rate, reducing the coke rateand remarkably enhancing the productivity of a blast furnace.

What is claimed is:

1. A method of blowing a reducing gas produced outside of a blastfurnace into the blast furnace in which the inside pressure variesdepending on the influence of the blast furnace and/or pressurevariations in the reducing gas blowing system, comprising the steps ofsupplying material including gaseous materials composed of fuel,auxiliary fuel and water vapor into a reducing gas generator,controlling the flow of gaseous materials supplied to the reducing gasgenerator, introducing the gaseous materials at a constant pressure forpassage through the flow control step so that the ratio of the pressureafter the gaseous materials have passed through the flow control step tothe constant pressure of the gaseous materials introduced for flowthrough the flow control step is less than the critical pressure ratio,withdrawing the reducing gas from the reducing gas generator andintroducing it to the blast furnace, and controlling the temperature ofthe reducing gas before it is introduced into the blast furnace.

2. A method, as set forth in claim 1, wherein the step of controllingthe temperature of the reducing gas includes separating a part of thereducing gas Withdrawn from the reducing gas generator and contactingthe separated reducing gas with a lower temperature reducing gas to forma reduced temperature reducing gas and maintaining the reducedtemperature reducing gas at a controlled fiow rate and mixing it withthe remainder of the reducing gas withdrawn from the reducing gasgenerator 1 1 to control the temperature at which the reducing gas isintroduced into the blast furnace.

3. A method, as set forth in claim 1, wherein the step of controllingthe temperature of the reducing gas includes supplying from a separatesystem at a controlled flow rate a reducing gas at a lower temperaturethan the reducing gas withdrawn from the reducing gas generator, andmixing the lower temperature reducing gas with the reducing gas from thereducing gas generator for controlling "the blowing temperature of thereducing gas into the blast furnace.

4. A method, as set forth in claim 1', wherein the step i of controllingthe temperature of the reducing gas includes cooling in a heat exchangera part of the reducing gas withdrawn from the reducing gas generator,cooling the other part of the reducing gas withdrawn from the reducinggas generator by contacting it with cooling water to produce a lowertemperature reducing gas, and mixing the lower temperature reducing gasin a controlled flow with the reducing gas cooled in the heat exchangerto control the blowing temperature of the reducing gas into the blastfurnace.

5. A method, as set forth in claim 1, wherein the step of controllingthe temperature of the reducing gas includes cooling the reducing gaswithdrawn from the reducing gas generator in a heat exchanger, andmixing a lower temperature reducing gas from a separate system at acontrolled rate into the reducing gas cooled in the heat exchanger forcontrolling the blowing temperature of the reducing gas to the blastfurnace.

6. A method, as set forth in claim 1, including the steps of diverting aportion of the reducing gas from its path of flow to the blast furnace,cooling the diverted flow of reducing gas, and discharging the cooleddiverted gas to a source other than the blast furnace.

References Cited UNITED STATES PATENTS 2,790,711 4/1957 Sellers et a175-42 X 2,577,730 12/1951 Benedict 75-35 3,375,098 3/1968 Marshall 75-353,458,307 7/ 1969 Marshall 75-42 3,236,628 2/1966 Bogandy 75-423,418,108 12/1968 Von Stroh 75-41 X 3,454,395 7/1969 Von Stroh 75-41 X2,740,701 4/1956 Tenny 48-191 X 3,210,181 10/1965 Manny 75-41 3,233,9872/1966 Hepburn 48-191 X 3,193,378 7/1965 Peet 75-35 3,591,364 7/1971Reynolds 75-35 X FOREIGN PATENTS 985,577 3/1965 Great Britain 75-42OTHER REFERENCES Dean: Article in Blast Furnace and Steel Plant, May1961, p. 417.

Bureau of Mines RI. 5621, Melcher et al., 1960, pp. 5-7.

Perry: Chem. Engin. Hdbk., 4th ed., McGraw-Hill, 1963, pp. 5-9 thru5-12.

L. DEWAYNE RUTLEDGE, Primary Examiner M. J. ANDREWS, Assistant ExaminerUS. Cl. X.R. 266-28

